[meteorite-list] Evidence Found for Large Impact Crater Off the Coast of Antarctica

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Mar 17 13:26:36 2006
Message-ID: <200603171707.k2HH7GR09362_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/1/hi/sci/tech/4816794.stm

Space impact clue in Antarctica
By Paul Rincon
BBC News
March 17, 2006

Evidence for what may be a large and relatively recent impact crater has
been found off the coast of Antarctica.

Scientists say the evidence, if correct, points to a space rock some 5km
across having crashed into the Ross Sea about three million years ago.

This could have generated a huge tsunami, according to a member of the
team investigating the collision.

Details were reported at the Lunar and Planetary Science Conference in
Houston, Texas.

Glass hints

Researchers from the Lamont-Doherty Earth Observatory in New York have
been studying a 100km-wide depression, known as Bowers Crater, under the
Ross Sea.

Team members examined cores drilled from around the area to look for
evidence of an impact.

In the cores, they found microscopic glassy grains shaped like
teardrops, spheres and dumbbells which are collectively known as tektites.

Some scientists believe these are created when rock fragments are hurled
high up into the atmosphere by the impact of a large meteoroid or
asteroid, and then partially re-melt as they fall back to the ground.

Other glasses were also found. These are thought to have been formed by
cooling of the melted rock and sediment. Similar glasses can be formed
through volcanism, but the Ross Sea specimens seem to have a distinct
structure under the microscope.

Wave trace

The findings alone do not prove there was an impact in the area a few
million years ago, but team member Dallas Abbott says she hopes to
search the core material further for a mineral called shocked quartz.

This type of quartz can be distinguished from normal quartz by
characteristic lines visible under the microscope which are thought to
be formed by the intense pressure of an impact.

The presence of this mineral is considered most diagnostic of a space
collision.

Dr Abbott told the BBC News website that an impact in the Ross Sea would
have generated a "pretty big tsunami".

The waves could have crashed against the shores of South America; but,
she added, the geological history of that continent made it unlikely
that evidence of this event would be found.
Received on Fri 17 Mar 2006 12:07:16 PM PST